1. Field of the Invention
The present invention relates to antenna devices including a base body which is a multilayer body formed by stacking and unifying a magnetic layer and non-magnetic layers and also relates to antenna modules which include this antenna device as a substrate and an RFIC chip unified with the substrate.
2. Description of the Related Art
Known examples of article identification and management systems include radio frequency identification (RFID) systems in which non-contact communication is performed between a reader/writer and an RFID tag, thereby transmitting information between an RFID system and the RFID tag. In the RFID system, predetermined information is transmitted/received between the RFID tag and the reader/writer.
In general, an antenna device (antenna coil) which uses a coil pattern as a radiation device is employed in an RFID system operating in an HF band represented by the 13.56 MHz band. This antenna coil, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2010-263486, includes a planar coil formed on the surface of a flexible substrate and a magnetic sheet bonded to the back surface of the flexible substrate.
However, in the case of the antenna coil disclosed in Japanese Unexamined Patent Application Publication No. 2010-263486, when the diameter of a coil is increased to increase a communication range, the size of an antenna is also increased, and in some cases, a null point may be generated along the center axis of a coil pattern. Further, since a magnetic sheet needs to be bonded to the flexible substrate in this antenna coil, a narrow gap may be generated between the flexible substrate and the magnetic sheet during a bonding process of the magnetic sheet. Then, the antenna characteristics of the antenna coil may be changed. Further, this structure of an antenna coil has a problem in that the flexible substrate and the magnetic sheet, which are originally separate and different members, are only bonded to each other and, hence, the antenna coil may warp or bend, depending on the materials of the substrate and the sheet.